Preheat oven to 350 F. Line a cookie sheet with parchment paper. Set aside.
In a bowl whisk together flour, baking powder, salt and baking soda. Set aside.
In a large bowl, cream together butter and cream cheese.
Mix in sugar, just until combined. (see note)
Mix in egg, vanilla extract and lemon zest.
Mix dry ingredients into wet ingredients.
Very carefully fold in blueberries, being careful not to break them open.
Drop dough by the heaping tablespoon full on the prepared baking sheet about 2 inches apart.
Bake for 12-15 minutes on the middle rack. (Check on them at the 11 minute mark. See note.)
Let cookies rest on pan for 1 minute before moving to a cooling rack to finish cooling.
Store cooled cookies in an airtight container.